When taking a picture using an electronic flash unit and color print film in the camera, an undesirable phenomenon known as the red-eye effect may occur. The red-eye effect is typified by the pupils in the eyes of the person being photographed coming out red-tinted on a color print made from the exposed film. It is attributed to the flash light from the electronic flash unit being reflected by the retinas, through the pupils, of the eyes of the person being photographed. Numerous capillary blood vessels around the retinas are the source of the red tinting of the pupils.
It is known to for the electronic flash unit to provide a brief pre-flash light emission before shutter opening to make an exposure and before the main flash light emission when the shutter is open. The pre-flash light emission is subject-conditioning, as compared to the main flash light emission which illuminates the subject during exposure. The pre-flash light emission causes the pupils in the eyes of the person being photographed to contract, and it precedes the shutter opening and the main flash light emission by a time delay such as 0.35-0.75 seconds. This time delay is sufficient to ensure a substantial reduction in the size (diameter) of the pupils. When the main flash light emission reaches the contracted pupils, less light is able to enter them and the red-eye effect is thereby substantially prevented or minimized.